This application claims the benefit of Japanese Patent Application No. 2004-326030, filed Nov. 10, 2004. The entire disclosure of the prior application is hereby incorporated by reference herein in its entirety.
Aspects of the invention can relate to an image display device having a liquid crystal panel used to display a still image and a moving image, and a method of driving the liquid crystal panel.
A related art image display device with a liquid crystal panel not only takes the place of a CRT (cathode-Ray Tube) and are used as a display for a personal computer in most cases, but they can also be utilized as a display device of television set or a projection type display device (liquid crystal projector).
In the principle on which an image display device expresses a tone, the change in light transmissivity in response to a voltage level applied to each pixel is utilized. However, the response speed at which the light transmissivity is changed with respect to the applied voltage actually is slow and as such, degradation of image quality including tailing and blurring arises particularly in displaying a moving picture.
For example, the color standard of analog television system of NTSC (National Television Standards Committee), which is typically used in U.S.A., Japan, etc., requires to display 29.97 frames per second. That is, this means that the time involved in displaying one frame is about 33 msec. However, it has been known that a typical active matrix type liquid crystal panel needs, as its usual response time, 20 to 30 msec. Hence, simply supplying a drive signal (voltage) at a timing desired for display to each pixel of the liquid crystal panel does not necessarily allow an intended transmissivity to be achieved.
As a method to prevent the degradation of quality for display a moving image due to such response characteristic, it has been suggested to utilize the property that liquid crystal materials have in general, the larger the change in the applied voltage is, the higher the response speed reaches. Such suggestion is made, for example, in the following documents: Japanese Patent No. 2650479; Japanese Patent Application Publications JP-A-2001-331154; and JP-A-2004-246118.
A method disclosed in Japanese Patent No. 2650479 includes: predetermining a variable transmissivity curve based on the mathematical expression that associates applied voltages with response times; storing the variable transmissivity curve in a data table; and making a corrector refer to a correction value derived from the curve and correct a voltage so as to establish a correspondence with a required transmissivity. However, according to the method, the variable transmissivity curve is estimated from a plurality of fields (successive three or more fields) to make the correction based on the estimation and as such, all the parts of the variable transmissivity curve on the plurality of fields, which are necessary for the estimation, will be kept in a table for each pixel. Therefore, large capacities of storage means including a ROM (Read Only Memory) are required for strict control. In addition, when it is desired to cope with various correction patterns, tables exclusively for such patterns must be prepared.
A method disclosed in JP-A-2001-331154 has been suggested to solve the above problems. According to the method, a corrected amount is selected based on the difference between a video signal for the immediately preceding field and a video signal for a current field, on which the operation of addition or multiplication is performed.
However, according to the method, only the information concerning one field is used and as such, there is the case where image degradation cannot be surely prevented. In such case, depending on the situation, an adverse effect such as noise arises, or a sufficient correction effect cannot to be obtained.
In JP-A-2004-246118, a suggestion to overcome the disadvantage of the method disclosed in JP-A-2001-331154 is made. However, according to the suggestion, a sufficient correction effect cannot be obtained in principle because only video signals for current and immediately preceding fields are used for the correction.